ISSN:
1435-1528
Keywords:
Key words Stokes–Einstein equation
;
Brownian motion
;
Complex fluids
;
Linear viscoelastic moduli
;
Particle diffusion
;
Estimation methods
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Abstract We obtain the linear viscoelastic shear moduli of complex fluids from the time-dependent mean square displacement, 〈Δr 2(t)〉, of thermally-driven colloidal spheres suspended in the fluid using a generalized Stokes–Einstein (GSE) equation. Different representations of the GSE equation can be used to obtain the viscoelastic spectrum, G˜(s), in the Laplace frequency domain, the complex shear modulus, G *(ω), in the Fourier frequency domain, and the stress relaxation modulus, G r (t), in the time domain. Because trapezoid integration (s domain) or the Fast Fourier Transform (ω domain) of 〈Δr 2(t)〉 known only over a finite temporal interval can lead to errors which result in unphysical behavior of the moduli near the frequency extremes, we estimate the transforms algebraically by describing 〈Δr 2(t)〉 as a local power law. If the logarithmic slope of 〈Δr 2(t)〉 can be accurately determined, these estimates generally perform well at the frequency extremes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s003970000094
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